This invention relates to hydraulically or pneumatically actuated muscles, that is, devices which convert a fluid pressure into a tensive force. The invention is more specifically directed to structure for biasing the muscle to its elongated or extended state. The invention is also directed to the serviceable attachment of the distal muscle terminator to its associated control cable.
Hydraulic muscles can be favorably employed in an elongated flexible probe such as a borescope or endoscope for actuating its articulation or steering section. With the use of hydraulic muscles, the conventional long steering cables can be eliminated. This use of a hydraulic muscle in a borescope or endoscope is described in U.S. patent application Ser. No. 357,806, now U.S. Pat. No. 4,962,751 filed May 30, 1989, and having a common assigned herewith. Another fluid dynamic muscle in a borescope or endoscope is described in U.S. Pat. No. 4,794,912, granted Jan. 3, 1989. Fluid dynamic articulation and steering for a borescope or endoscope offers a distinct improvement over the conventional system of steering cables, permitting much more accurate and precise positioning of the viewing end of the instrument within the cavity to be inspected.
The hydraulic or fluid dynamic muscle is made of an elongated tubular bladder which is encased in an elongated tubular braid member disposed over it. Terminators are provided at the proximal and distal ends of the muscle to seal the ends of the bladder and to provide a place for mechanical attachment between the ends of the braid member and the mechanical members to which they are to transfer force, e.g., a cable or a muscle sheath. The braid permits the bladder within the muscle to expand laterally when hydraulic pressure is applied to it. However, as the braid and bladder expand radially, the braid contracts axially and generates an axial tensive force.
The fluid dynamic muscles are used in pairs, with one of the muscles being actuated to deflect the borescope steering section in one direction (i.e. to the left) and the other muscle being actuated to deflect the steering section in the other direction (i.e. to the right). With this arrangement the tension from the muscle that is actuated extends the muscle that is not being actuated and expels the fluid from it. The bladder and braid alone typically are not effective to stretch the muscle back to an elongated state when the hydraulic or pneumatic pressure is relieved. Therefore, there is a constant tension on both steering cables of each pair of cables. This can make steering somewhat difficult, can reduce the amount of articulation of the steering section, and can require higher pressures to be employed than is desirable in view of the need to avoid leakage of hydraulic fluid from the muscles.
Also, under current techniques, access to the muscle terminator that connects to the cable terminator is difficult, once the muscle is installed. Further, it is difficult to detach and reattach the cables to the muscle terminators, and special tools may be required to do so.